1. Field of the Invention
The present invention relates to a reflective real specular image forming element forming a real image (real specular image) of an observed object in a space of a viewer side, and more particularly to a display device using a dihedral corner reflector array optical element.
2. Description of the Related Art
There have been suggested a display device for allowing a viewer to see a real image (real specular image) of an observed object in air (see Patent Publication WO2007-116639).
Specifically, such a display device comprises a reflective real specular image forming element performing the formation of a real image (real specular image) of an observed object in a space of a viewer side; and the observed object disposed in a space opposite to the viewer side with respect to the reflective real specular image forming element.
The document WO2007-116639 discloses a reflective real specular image forming element (so-called the dihedral corner reflector array optical element) in which a plurality of unit optical elements (each so-called as dihedral corner reflector) are arranged regularly on one plane of the element face wherein each of unit optical elements has two orthogonal mirror surface which are perpendicular to each other. FIGS. 1, 2 and 3 shows a schematic plan view, an enlarged partial cutaway perspective view and a cross-section view which illustrate specific embodiments of the dihedral corner reflector array optical elements disclosed by WO2007-116639 respectively.
FIG. 1 shows as a specific embodiment of the dihedral corner reflector array optical element which specifically utilizes inner walls 61a and 61b (mirror surfaces) of each square shaped hole made in a substrate 60 while penetrating the main face thereof as a dihedral corner reflector 61 disclosed by WO2007-116639. As shown in FIGS. 1 and 2, the dihedral corner reflector array optical element 66 comprises the substrate 60 of a thick flat plate and a plurality of square shaped holes made therein so as to physically and optically penetrate the thick thickness thereof perpendicular to the main face thereof where mirror surfaces 61a, 61b of two orthogonal flat internal sides within each penetrating hole are formed as the dihedral corner reflector 61. As shown in FIG. 3, the dihedral corner reflector (mirror surfaces 61a, 61b of the penetrating hole) reflects twice a ray of light emitted from a point light source (o) while passing trough the substrate 60 with a bend.
Further as shown in FIG. 4, there is also disclosed by WO2007-116639 a dihedral corner reflector array optical element comprising a plurality of transparent cubic shape tubular bodies 51 each perpendicularly protruding in the thickness direction (Z) from the surface of the substrate 60 (XY plane) made of a transparent material from wherein inner wall surfaces (mirror surfaces 61a and 61b) of the transparent cubic shape tubular body 51 are used for the dihedral corner reflector 61, wherein the tubular bodies are laid out in a grid pattern.
In a plurality of the arranged dihedral corner reflector of the dihedral corner reflector array optical element, since each mirror surface is disposed perpendicularly to the element face, light (emitted from the observed object existing on the one side of the element face) is reflected twice by the dihedral corner reflector during passing therethrough, and then by all light passed through the element, a real image is formed in a space of observed object absent on the other side of the element face. Namely, the dihedral corner reflector array optical element performs the formation of real image in such a manner that the real image of the object exists symmetrical to the observed object with respect to the element face (so-called a plane of symmetry) of the dihedral corner reflector array optical element.